High purity filtration of aqueous media, such as in the fields of biotechnology, chemistry, electronics, pharmaceuticals and the food and beverage industries requires the use of sophisticated filter modules that are not only capable of a high degree of separation, but that will tend to prevent contamination of the environment, of the medium to be filtered, and of the filtrate. Because the degree of filtration achieved results in the removal of not only objectionable materials and microorganisms, but also of gases present in the medium to be filtered, and because commercial protocol calls for periodic checking of the integrity of the module, such modules are fabricated with the goal of withstanding a build-up of gas pressure and yet operate efficiently and be leakproof. However, as will be noted below, current technology has not yet been able to successfully achieve this goal.
Because the build-up of gas pressure within the filter module tends to reduce the effective surface area of the filter element of the module, gas pressure within the module must be periodically released. To be capable of periodically releasing this build-up of gas (often referred to as "degassing"), such filter units are often equipped with one or more pressure relief valves.
There are however, several drawbacks with the pressure release mechanisms that are currently available with known high purity filter modules. Specifically, for example, when the integrity of the module is checked by tests such as the bubble point, the pressure retention, or the diffusion tests, the module is rendered gas-tight and the inside is pressurized by means of gas-tight test apparatus such as that made and sold under the trade name "Sartocheck" by Sartorius AG of Goettingen, Germany. The pressurization causes at least a small amount of the aqueous medium to be filtered to leak from the pressure relief valve or valves. Such leakage causes contamination of the outside of the filter module housing, environmental pollution when hazardous materials are being filtered, and potential contamination of the inside of the module and hence of the filtrate by contact with microorganisms in the environment exterior to the module.
Accordingly, it is an object of the present invention to provide a pressurizable high purity filter module for filtering aqueous media which is leakproof during degassing and pressurized testing of the module, which in turn provides the advantages of security against contamination of the module itself, of the filtrate and of the medium to be filtered, and further provides security against environment pollution.
This object and others will be understood from the detailed description of the preferred embodiment of the present invention set forth below.